Over the last ten years or so, drug infusion pumps have been developed which can be implanted in the body and remain there for a relatively long period of time to dispense small measured doses of medication to a selected infusion site in the body. The pump chamber can be refilled with infusate without having to remove the pump from the body by injecting additional infusate transcutaneously through a penetrable septum in the pump wall which septum is located directly under the patient's skin. In some pumps, the refilling of the device also recharges the device's power source. The main advantage of dosing devices of this type is that medication can be routed to the site where it is needed, rather being injected into the bloodstream so that it spreads throughout the body.
Some implantable infusion apparatus have dual pumping chambers enabling them to dispense different infusate concentrations or even different infusates to the same or different infusion sites in the patient's body. The two pumping chambers are purged and refilled independently by way of separate inlet ports at different locations on the pump wall, each port having its own needle-penetrable septum located underneath the patient's skin. An example of this type of pump is disclosed in U.S. Pat. No. 4,258,711.
Another known implantable infusate-dispensing apparatus has, instead of a second pumping chamber, an injection portal incorporated into the pump wall. This portal is basically a chamber with an outlet tube leading to an infusion site in the patient's body and an inlet port closed by a needle-penetrable septum located underneath the patient's skin and which is accessible by transcutaneous injection. This type of device dispenses a continuous flow of infusate to the patient. Then, if a bolus dose or supplemental medication is required, this is administered by percutaneous injection into the portal. Such a device can also be used for blood withdrawal. Apparatus of this type is shown, for example, in U.S. Pat. No. 4,496,343.
In some cases, a patient's drug protocol may call for periodic injection of two different drugs over a long period of time. In this event, such a patient might be fitted with two or more implanted injection portals so that a particular infusate can be supplied to two different sites in the body or so that different drugs can be routed to the same infusion site.
It is apparent from the foregoing that once these implantable pumps and portals have been surgically implanted in the patient's body, the positions of their various inlet ports are more or less fixed with respect to the overlying skin area of the patient. Therefore, each time the physician must inject additional infusate into a particular inlet port in the implanted apparatus, he must penetrate or puncture the skin at substantially the same location. Over a period of time, then, a patient may receive many such needle penetrations in order to service the implanted device.
In this connection, we should mention that when introducing infusate into an implanted pump or portal, the normal procedure is to insert a cannula or needle into that device's inlet port and allow the drug in the reservoir to flow out (i.e. the reservoir is at a higher pressure than the needle or cannula lumen). Then, when the reservoir is empty, a fixed volume of the fresh infusate is injected into the pump or portal through the needle, after which the needle is withdrawn. It is apparent, therefore, that this refilling procedure is a time consuming process that requires the patient to remain still while the needles penetrating his body introduce and/or drain the various fluids from the infusion device implanted in his body. In many instances this procedure is performed in a clinic or physician's office or on a hospital outpatient basis. Therefore, each office visit can be quite time consuming and expensive.
Another disadvantage of the prior techniques for servicing plural port implantable devices of this general type is their propensity for being refilled with the wrong fluid. More particularly, after the device is implanted, its position may change somewhat relative to a fixed spot on the patient's skin surface due to changes in the patient's body weight, for example. Therefore, when refilling or purging the device, it is quite easy for a nurse to insert a needle into the wrong inlet port if she is not very careful. In a dual-chamber infusate pump, for example, this could result in the basal reservoir of the pump being refilled with bolus infusate and the bolus reservoir being charged with lower concentration basal infusate, or it could result in one reservoir of that pump being emptied and filled twice and the other reservoir not being serviced at all.
It would be desirable, therefore, if the number and duration of transcutaneous injections required to access or to service an implanted pump or portal could be minimized, along with the potential for servicing errors. This would not only reduce the risk of infection to the patient, it would also reduce the incidence of epidermal problems associated with implanted access or drug infusion devices of this type, and it would certainly reduce the physical and emotional stress on a patient required to have such an implanted device.